Speed control for a pumping system

ABSTRACT

A wastewater pumping system includes a centrifugal pump operatively connected to an electric motor via a coupling. The speed of the electric motor is automatically varied responsive to the head or load realized by the pump of the system as it varies with the composition of the slurry mixture. A variable frequency drive is operatively connected to the motor and the electrical power supply that affects a shift or change in electrical frequency delivered to the electrical motor so that the speed of the motor and consequently the pump is varied. This allows the electrical power deliver to the system to remain substantially unchanged for varying loads realized by the pump.

I. BACKGROUND OF THE INVENTION

[0001] A. Field of Invention

[0002] The present invention relates to the art of wastewater pumps and more specifically to a speed control device for operating the wastewater pumps.

[0003] B. Description of the Related Art

[0004] Wastewater pumping systems are known to use centrifugal pumps. Centrifugal pumps work well to maintain flow rate. However, when pressure or head is increased in a wastewater system the flow rate decreases. Therefore, the centrifugal pump does not lend itself to higher head applications.

[0005] A typical centrifugal pump functions based on speed of the impeller or kinetic energy of the fluid being pumped based on the impeller speed. This is contrasted with positive displacement pumps, such as piston pumps or the like. Typically, the centrifugal pump is powered by an electric motor. That is to say that the motor, generally an AC motor, rotates the impeller of the pump at a specific speed based upon the operating characteristics of the motor, such as the number poles in the motor and the frequency of the power being supplied to the motor. If the load realized by the impeller increases, the impeller will want to slow down. However, the motor will naturally try to maintain the characteristic speed of the motor by drawing additional current to compensate for the increase in load seen by the impeller. This results in increased current and power being drawn by the centrifugal pumping system.

[0006] What is needed is a self-regulating speed controlling device, for maximizing pump performance and maintaining constant current, which allows the centrifugal pump to be installed in a variety of environments where higher heads, as well as lower operating heads are exhibited.

[0007] Other objects and advantages of the invention will appear from the following detailed description of the preferred embodiment of the invention with reference being made to the accompanying drawings.

II. BRIEF SUMMARY

[0008] There is provided a centrifugal pump that is operatively connected to slurry conduits as part of a wastewater pumping system. The pump has an inlet for connecting to a first slurry conduit, which in turn is communicated to a reservoir or source for providing an associated slurry mixture to the system. The pump also includes an outlet connected to second slurry conduit through which the slurry mixture is propelled to a discharge tank. An electric AC motor is directly coupled to the pump for use in providing rotational power to drive the pump thereby propelling the slurry mixture. Inherent to the pumping system, head is developed and realized by the pump that is based upon the elevation or distance that the slurry mixture is being pumped, as well as inconsistencies in the composition of the slurry mixture. Still other characteristics of the system contribute to the head, which are well known in the art but will not be discussed further at this point. As the head increases, which may be due to other pumping system outputs being dumped into the same conduit or inconsistencies in the slurry mixture, a self regulating speed controlling device is operatively electrically communicated between an electrical power source or electrical mains and the motor that alters the speed of the motor and hence the pump in response to the change in load or head realized at the pump. The controlling device includes a variable frequency drive that may alter the frequency of the electrical power thereby changing the speed of the motor and the pump respectively. In this manner, as the load realized by the pump increases, the controlling device alters the electrical power frequency to speed up the motor thereby holding constant the electrical current drawn by the pumping system and vice versa for decreases in pump loads. In other words, the pumping system automatically changes the speed that the motor rotates a propeller in the pump responsive to the load realized by the pump.

[0009] It is an object on the present invention to provide a wastewater pumping system including a pump, a motor and a controlling device, wherein the controlling device alters the speed of the motor responsive to the load realized by the pump.

[0010] It is another object of the present invention to provide a wastewater pumping system including a pump, a motor, a controlling device and a load current sensor that automatically adjusts the frequency of the electrical power received by the controlling device for delivery to the motor responsive to the change in load realized by the pump as determined by a load current sensor.

[0011] It is yet another object of the present invention to provide a wastewater pumping system including a centrifugal pump, an AC Induction motor, a variable frequency drive, a load current sensor, reference signal controlling means and selectively adjustable switching means, for use in selecting one of a plurality of reference signals whereby substantially constant current is maintained with respect to the selected reference signal, while the speed of the motor is automatically adjusted responsive to the output from the sensor.

III. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:

[0013]FIG. 1 is a schematic representation of a wastewater pumping system.

[0014]FIG. 2 is a perspective view of an electric motor and wastewater pump with a control panel.

[0015]FIG. 3 is a schematic representation of a reference signal storing means.

[0016]FIG. 4 is a pump characteristic comparison chart.

[0017]FIG. 5 is a schematic representation of a PWM signal.

[0018]FIG. 6 is a partial schematic representation of a centrifugal with internal rotating impeller.

IV. DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting the same, FIG. 1 depicts a schematic representation of a wastewater pump 1 operatively connected to a supply source 3 of slurry mixture 4 via a slurry inlet conduit 6. The wastewater pump 1 may include an inlet 7 for use in receiving the slurry mixture 4 from the slurry conduit 6. The wastewater pump 1 may also include an impeller 19, shown in FIG. 6, for use in pumping the slurry mixture 4 via an outlet 9 to a discharge tank 13 or other storage means. In this manner, the slurry mixture 4 is transmitted through the body 2 of the pump 1. The outlet 9 of the wastewater pump 1 may be connected to the discharge tank 13 via slurry outlet conduit 16. It is noted that any configuration of supply source and discharge tank storage means for containing the slurry mixture may be chosen with sound engineering as is appropriate for wastewater pumping systems. In the preferred embodiment, the wastewater pump 1 may be a centrifugal pump 18. However, any pumping means may be chosen with sound engineering judgment as is appropriate for a wastewater pumping system including progressive cavity pumps. It is expressly noted that the invention as described herein is not intended to be limiting by the type of pumping device or configuration of the pumping system depicted in the embodiments but shall be construed as applicable to any configuration of pumping mechanism as is appropriate for wastewater pumping systems and other pumping systems as well.

[0020] With reference now to FIG. 2, a wastewater pump 1 is depicted, which as stated may be a centrifugal pump 18. An electric motor 21 is shown coupled to the wastewater pump 1, via a coupler 22, for use in supplying power to drive the wastewater pump 1 at a specified rotational speed. In that the coupling of electric motors to pumping devices is well known in the art no further explanation will be offered at this point. In the preferred embodiment, the electric motor 21 may be an AC Induction motor 23 as will be discussed further in a subsequent paragraph. A control panel 27 is also shown having control componentry 28 contained therein for use in controlling the operation of the motor and hence the pump. The control panel 27 may include a main disconnect, one or more power transformers, over-current circuit protecting means, as well as other additional control componentry, not shown, as is appropriate for use in a control panel. In that the make-up of such control panels is well known in the art, no further explanation will be offered at this point.

[0021] With continued reference to FIGS. 1 and 2, as is well known in the art, power supplied to the electric motor 21 may be communicated via electrical conductors 31 that transmit electrical power from the control componentry 28 disposed in the control cabinet 27, which is further supplied from the electrical mains. It is expressly noted that any type (DC or AC), magnitude or frequency, of electrical power utilized by the motor may be chosen with sound engineering judgment as is appropriate for operating the electrical motor 21. It is also noted that by changing the speed of the motor 21, the speed of the impeller of the pump 1 may also change accordingly. The control panel 27 may include a motor speed control module 34. The motor speed control module 34 may be mounted within the control panel 27. It is also conceived in an alternate embodiment that the motor speed control module 34 may be contained in a separate enclosure mounted exterior to the control panel 27 such as in proximity to the pump and operatively electrically connected to the control componentry in a manner well known in the art. In the preferred embodiment, the motor speed control module 34 may include a selectively variable frequency controlling means 29 for use in selectively varying the frequency of electrical power that is delivered to the motor 21. The selectively variable frequency controlling means 29 may receive AC electrical power from a transformer 30 located within the control panel 27, which may initially receive power from the electrical mains. It is noted that main power may be connected to the transformer 30 for adjusting the magnitude of voltage being communicated to the selectively variable frequency controlling means 29. Additionally, the power may also be converted to DC power for use by the selectively variable frequency controlling means 29. However, any means of conditioning or communicating power to the selectively variable frequency controlling means 29 may be chosen with sound engineering judgment.

[0022] With continued reference to FIG. 2 and now to FIG. 5, as previously noted, the selectively variable frequency controlling means 29 receives electrical power. The selectively variable frequency controlling means 29 subsequently delivers a conditioned power signal 42, which is communicated via electrical conductors 31, to the motor 21. In the preferred embodiment, the conditioned signal 42 may be Pulse Width Modulated (PWM) signal 42, represented in FIG. 5. Any duty cycle, frequency and magnitude combinations may be chosen with sound engineering judgment as is appropriate for controlling a motor 21 and as will be discussed in a subsequent paragraph. In other words, the power delivered from the mains is received by the selectively variable frequency controlling means 29 and selectively conditioned for use in controlling the motor 21. It is expressly noted here that selectively variable frequency controlling means 29 may selectively vary the frequency of the PWM signal 42. In other words, the selectively variable frequency controlling means 29 may be a Variable Frequency Drive 29 a or VFD 29 a. The variable frequency controlling means 29 may include a sensing means 43 for sensing the current load drawn by the motor 21. In the preferred embodiment, the sensing means 43 automatically determines when a change in the magnitude of current of the signal 42 has occurred and the VFD 29 a automatically adjusts the frequency of the PWM signal 42 so as to vary the speed of the motor 21 such that substantially constant power is drawn by the motor 21 during operation of the system. In other words, the VFD 29 a automatically selectively adjusts the speed of the motor 21, and consequently the pump 1, dependent upon the load of the pump 1 and hence the motor 21 in order to maintain substantially constant current being utilized by the system. Inasmuch, as Variable Frequency Drives are well known in the art, no further explanation will be discussed at this point. It is noted that the pump 1, motor 21 and control panel 27 with VFD 29 a and supporting components constitute a wastewater pump assembly 1 a.

[0023] With reference now to FIGS. 4 and 6, a typical centrifugal pump functions based on speed of the impeller or kinetic energy of the fluid being pumped based on the impeller speed. This is contrasted with positive displacement pumps, such as piston pumps or the like, which may function to provide constant fluid pressure. Typically, the centrifugal pump is powered by an electric motor. That is to say that the motor, generally an AC motor, rotates the impeller of the pump at a specific speed based upon the operating characteristics of the motor, such as the number poles in the motor and the frequency of the power being supplied to the motor. If the load realized by the impeller increases, the impeller will want to slow down. However, the motor will naturally try to maintain the characteristic speed of the motor by drawing additional current to compensate for the increase in load seen by the impeller. This results in increased current and power being drawn by the centrifugal pumping system. In the preferred embodiment, it is desirable to maintain constant current and constant voltage over the operating range of the wastewater pump assembly 1 a. Therefore, the sensing means 43 senses increased current drawn by the motor 21 when the pump 1 realizes increased head H. The sensing means 43 then feeds back signals to the VFD 29 a, wherein the VFD 29 a maintains the magnitude of current presently being drawn while increasing the frequency of the PWM signal 42. Similarly, with a decrease in Head H, the sensing means 43 senses a decrease in current and the VFD 29 a may consequently decrease the frequency of the PWM signal 42 while maintaining substantially the same magnitude of current. In this manner, an increase in Head H results in the automatic adjustment of the VFD 29 a to increase the frequency of power signal 42 seen by the motor, which increases the speed of the motor and the impeller. Likewise, decreasing the head H decreases the frequency of the signal 42. In this manner, when a change in the head H occurs, the magnitude of electrical current is substantially constant although the frequency of the motor varies commensurate with the magnitude and direction of change in the head H. In essence, for a given magnitude of current being drawn by the system, there is a corresponding Head versus Flow chart, such as is depicted in FIG. 4, relative to the given magnitude of current.

[0024] With reference now to FIGS. 2 and 3, it is desirable to selectively operate the pump 1 at different levels of substantially constant current in a manner consistent with the previous discussion. Therefore, a reference signal representing a given magnitude of substantially constant operating current must be available for reference by the VFD 29 a to maintain a selectively chosen constant current during operation. As it is desirable to utilize the present invention in a plurality of environments, a method for selecting one of a plurality of reference signals will be discussed presently. In the preferred embodiment, the VFD 29 a may include a reference signal storing means 45, which may be an Integrated Circuit 45 shown in FIG. 3, that may store a plurality of reference signals used by the VFD 29 a. It is noted that each signal in the storing means 45 corresponds to magnitude of constant operating current. In this manner, the VFD 29 a may reference one of the signals for use in maintaining a specific magnitude of constant operating current as previously discussed. The Integrated Circuit 45 may be a Programmable Read-Only-Memory chip 45 or PROM 45 wherein a plurality of reference signals may be selectively “burned” into the PROM 45. However, any means of storing reference signals for use by the VFD 29 a in maintaining constant operating power may be chosen with sound engineering judgment. In this manner, the pump 1 may be operatively configured to operate in various modes or in various environments by referencing different signals stored in the reference signal storing means 45. That is to say that the VFD 29 a, during operation, automatically maintains a substantially constant magnitude of current with respect to one of the reference signals stored in the reference signal-storing means 45. A selectively adjustable switching means 46, shown in FIG. 2a, may also be included in the control panel circuitry and operatively communicated with the VFD 29 a, which may be selectively adjusted by an operator to cause the VFD 29 a to reference one of the different signals stored in the reference signal storing means 45. In the preferred embodiment, the selectively adjustable switching means 46 may be a Dip Switch 46 having eight (8) binary signal switches. The Dip Switch 46 may be operatively connected to the VFD 29 a so as to select one of the signals stored therein for reference by the VFD 29 a during operation. In other words, when an operator adjusts the Dip Switch 46, the internal VFD circuitry will detect the Dip Switch setting and, in a predetermined manner, reference one of the signals stored in the reference signal storing means 45. Thereafter, the wastewater pump assembly 1 a is selectively configured to automatically substantially maintain the operating current of the motor with respect to the reference signal chosen by the operator, which may correspond to a specific operating environment. In this manner, the wastewater pump assembly 1 a may be selectively configured for use in a variety of wastewater pumping scenarios by switching into or out-of engagement the individual binary signal switches.

[0025] While specific embodiments of the invention have been described and illustrated, it is to be understood that these embodiments are provided by way of example only and that the invention is not to be construed as being limited thereto but only by proper scope of the following claims. 

I/we claim:
 1. A fluid pumping system, comprising: a pump operable to pump associated fluid; a motor operatively coupled to drive the pump; and, a controlling device electrically communicated between an associated electrical power source and the motor, wherein the controlling device is operable to change the speed of the motor responsive to a change in the load of the pump, while maintaining substantially constant voltage and constant current.
 2. The pumping system of claim 1, wherein the speed of the motor is changed by adjusting the frequency of electrical power being supplied to the motor.
 3. The pumping system of claim 1, wherein the controlling device includes: variable frequency controlling means operably communicated to deliver variable frequency electrical power to the motor.
 4. The pumping system of claim 3, further comprising: a sensor operatively communicated to the variable frequency controlling means, and, wherein the variable frequency controlling means delivers variable frequency electrical power to the motor responsive to the sensor output.
 5. The pumping system of claim 4, wherein the sensor is a load current sensor for use in feeding back load current being drawn by the pumping system.
 6. The pumping system of claim 1, further comprising: a reference signal storing means for use in storing a plurality of reference signals, the reference signal storing means being operatively communicated with the controlling device; and, wherein the magnitude of constant current is maintained relative to one of the plurality of reference signals stored in the reference signal storing means.
 7. The pumping system of claim 6, further comprising: selectively adjustable switching means for use in selecting said one of the plurality of reference signals stored in the reference signal storing means, the selectively adjustable switching means being operatively communicated with the reference signal storing means.
 8. A wastewater pumping system, comprising: a centrifugal pump operable to pump an associated wastewater slurry; an AC motor operatively coupled to drive the pump; and, a control panel operatively connected drive to the AC motor, the control panel being operable to receive associated electrical input power, the control panel including: a load current sensor, a variable frequency drive operatively communicated to the AC motor and the load current sensor, and, wherein the variable frequency drive is operable to change the speed of the motor responsive to the output of the sensor, while maintaining substantially constant voltage and constant current.
 9. The pumping system of claim 8, further comprising: a reference signal storing means for use in storing a plurality of reference signals, the reference signal storing means being operatively communicated with the variable frequency drive; and, wherein the magnitude of constant current is maintained relative to one of the plurality of reference signals stored in the reference signal storing means.
 10. The pumping system of claim 9, further comprising: selectively adjustable switching means for use in selecting said one of the plurality of reference signals stored in the reference signal storing means, the selectively adjustable switching means being operatively communicated with the reference signal storing means.
 11. A method for controlling a pumping system, the steps comprising: providing a centrifugal pump operable to pump an associated slurry, an AC motor operatively coupled to drive the pump, a load current sensor; and, variable frequency controlling means operatively communicated to the AC motor and the load current sensor, operating the pumping system; sensing a change in the load current of the motor; automatically varying the frequency of the electrical power responsive to the change in the load of the pump while maintaining substantially constant current supplied to the AC motor.
 12. A method for controlling a wastewater pumping system, the steps comprising: providing a centrifugal pump operable to pump an associated wastewater slurry, an AC Induction motor operatively coupled to drive the pump, a load current sensor, a variable frequency drive operatively communicated to the AC motor and the load current sensor, a reference signal storing means for use in storing a plurality of reference signals, the reference signal storing means being operatively communicated with the variable frequency drive, and, selectively adjustable switching means for use in selecting one of said plurality of reference signals stored in the reference signal storing means, the selectively adjustable switching means being operatively communicated with the reference signal storing means; selecting one of a plurality of reference signals; operating the pumping system; sensing a change in the load current of the motor; automatically varying the frequency of the electrical power responsive to the change in the load of the pump, while maintaining substantially constant current supplied to the AC Induction motor relative to said one of a plurality of reference signals. 